1. Field of the Invention
The present invention relates to a production method for producing a semiconductor device by growing a crystalline compound semiconductor for forming a functional device on a surface of a substrate of monocrystalline silicon.
2. Description of the Prior Art
Generally speaking, the compound semiconductor such as GaAs has advantages in that it has a higher electron mobility and a wider width of the forbidden band when compared with the element semiconductor such as Si or Ge and that it has a direct band gap.
Various devices drivable at a high speed such as infrared-emitting diode, semiconductor laser, ultrasonic transducer, GaAs FET and the like have been developed by utilizing these advantages of the compound semiconductor.
Also, various attempts for producing high performance composite LSI by forming compound semiconductor devices on a silicon wafer substrate have been made.
However, it is difficult to produce a GaAs layer having few lattice defect only by depositing GaAs on the monocrystalline silicon substrate since there is lattice misfit of about 4% between the silicon monocrystalline and GaAs monocrystalline.
In order to solve this problem, the following methods have been proposed.
(I) Method in which Ge layer is formed on a surface of a monocrystalline silicon substrate at first noticing the fact that Ge crystal has a lattice parameter almost same as that of GaAs crystal and, thereafter, GaAs layer is formed on the Ge layer (See, for example, JP-A No. 61-64119).
(II) Two steps growing method comprising the following steps:
step for growing thin GaAs layer of 100-200 .ANG. on a surface of a monocrystalline silicon substrate at a relatively low temperature of 400.degree..about.450.degree. C. as the first layer and PA1 step for forming the second GaAs layer at a temperature of 700.degree..about.750.degree. C. PA1 whereby the lattice misfit is relaxed by said first GaAs layer (See p 1 to p 6 of the material offered to the joint study session of 125-th committee and 145-th committee of the Japan Society for Promotion of Science which was held on Dec. 12, 1986).
(III) Method in which strained superlattice layers are formed on a surface of a monocrystalline silicon substrate in order to relax the lattice misfit and, thereafter, GaAs layer is formed on the strain superlattice layer (see p 12 to p 17 of the same mentioned in the item (II)).
(IV) Method in which an insulating layer of CaF.sub.2 or the like is formed on a surface of a monocrystalline silicon substrate with use of the epitaxial growing method and, then, GaAs layer is formed on said insulating layer (See p 36 to p 40 of the same mentioned in the item (II)).
However, these proposed methods have various disadvantages as follows:
In the first method (I), there is a problem of auto-doping which causes deterioration in characteristics of the functional device due to doping of Ge into GaAs.
Even in the two steps growing method (II), the dislocation density in the GaAs layer has a fairly large value of 10.sup.8 cm.sup.-2.
Further, in the third method (III), it is necessary to form strained superlattice layers of about ten layers and, due to this, the production process becomes complicated and takes a long time.
Also, no detailed result of research regarding the problem of the lattice misfit between the insulating layer and the GaAs layer has been reported until now.